Programs become unstable or do not start after you install an x64-based version of Windows on the same partition as a 32-bit version of Windows (896455)

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Dual-boot configurations that include an x64-based version of Windows and a 32-bit version of Windows are fully supported by Microsoft. However these operating systems must reside on separate drive partitions. In a dual-boot environment, you can run 16-bit programs on a 32-bit version of Windows. The 32-bit version of Windows also provides support for programs that use a 16-bit Setup program. However, programs that use a 16-bit Setup program are not supported in x64-based versions of Windows.

When you try to install an x64-based version of Windows on a partition that already contains a 32-bit version of Windows, the following warning appears in the text-mode Setup program:You chose to install Windows on a partition that contains another operating system. Installing Windows on this partition might cause the other operating system to function improperly.

Caution Installing multiple operating systems on a single partition is not recommended. To learn more about installing multiple operating systems on a single computer, see
http://www.microsoft.com/windowsxp/using/setup/learnmore/multiboot.mspx
using Internet Explorer.

• To continue using this partition, press C.
• To select a different partition, press ESC.

If you want to set up a dual-boot system, use the following best practices:

• Always install the 32-bit version of Windows first to make sure that the correct startup files are written to the root of the drive. If you overwrite the x64-based version of NT Loader (NTLDR) with the version of NTLDR that is included with 32-bit versions of Windows, this prevents the x64-based version of Windows from starting. The version of NTLDR that is included with x64-based versions of Windows is backward-compatible with the version of NTLDR that is included with 32-bit versions of Windows. The versions of NTLDR that are included with the 32-bit versions of Microsoft Windows XP and Microsoft Windows Server 2003 cannot start the current releases of x64-based versions of Windows.
• Do not install an x64-based version of Windows on the same partition as a 32-bit Windows installation. The x64-based versions of Windows use the same Program Files folder and the same Documents and Settings folder as 32-bit versions of Windows. Therefore, the contents of these directories may be replaced with 64-bit versions of the .dll and .exe files that are required by the 32-bit versions of Windows. If the 32-bit files are replaced, 32-bit programs and services may not start or may become unstable. If you unintentionally install the x64-based version of Windows on the same partition as an existing 32-bit version of Windows, back up as much data as possible. Then, format and reinstall both operating systems.

Technical support for Windows x64 editions

Your hardware manufacturer provides technical support and assistance for Microsoft Windows x64 editions. Your hardware manufacturer provides support because a Windows x64 edition was included with your hardware. Your hardware manufacturer might have customized the Windows x64 edition installation with unique components. Unique components might include specific device drivers or might include optional settings to maximize the performance of the hardware. Microsoft will provide reasonable-effort assistance if you need technical help with your Windows x64 edition. However, you might have to contact your manufacturer directly. Your manufacturer is best qualified to support the software that your manufacturer installed on the hardware.

For product information about Microsoft Windows XP Professional x64 Edition, visit the following Microsoft Web site: For product information about Microsoft Windows Server 2003 x64 editions, visit the following Microsoft Web site: